1. Technical Field
The present invention relates to a method of manufacturing an optical sheet, an optical sheet, a planar lighting apparatus, and an electro optical apparatus.
2. Related Art
Conventionally, a liquid crystal display apparatus is provided with a backlight which serves as a planar lighting apparatus that emits light in a planar manner. Such a backlight generally has a diffuser sheet as an optical sheet that diffuses light from a light source such as an LED over the entire back surface of the liquid crystal panel so as to suppress unevenness in brightness of the light for illuminating.
As a method of manufacturing such the diffuser sheet, there is known an applying method in which resin containing diffusing fine particles (for example, metallic fine particles or resin beads) are applied to one side surface of a sheet substrate, and the resin film thus applied is then cured. However, the above applying method has a difficulty in controlling the density distribution of the diffusing fine particles, that is, optical properties of the diffuser sheet (for example, intensity distribution or diffuser efficiency of the light diffused).
In view of the above, for the above method of manufacturing a diffuser sheet, there has already been made a propose to enhance the optical properties of the diffuser sheet (see, for example, JP-A-2004-157430). According to JP-A-2004-157430, there is proposed an ink jet method in which resin liquid droplets are discharged to one side surface of a sheet substrate, and the liquid droplets thus discharged are then dried and cured, thereby forming dots as protrusions having light diffusion properties. Further, dot forming position, dot size, and dot density distribution can be controlled depending on the volume of liquid droplets or the position at which liquid droplets are discharged, thereby making it possible for the one side surface of the sheet substrate to have predetermined optical properties.
However, in the above-mentioned diffuser sheet, its sheet substrate is made to have a thickness of between several tens of μm and several hundreds of μm so as to suppress the degradation of brightness of the liquid crystal apparatus (backlight). Moreover, according to the above-mentioned ink jet method, such the thin sheet substrates are sequentially moved and conveyed to the position where the liquid droplets are discharged.
As a result, in the ink jet method, when, for example, upon the movement and conveyance of the sheet substrate, an external stress, vibration or the like is applied to the sheet member of the sheet substrate, there occur positional deviation or mechanical deformation (flexure, distortion or the like) of the sheet substrate, thereby deteriorating the position accuracy of the depositing position of the liquid droplets. By extension, there was a problem in that the positional deviation of the dot forming position, variation in dot size or the like may occur, resulting in variation of the optical properties of each diffuser sheet.